JP6533663B2 - Ball screw and steering device - Google Patents

Description

  The present invention relates to a ball screw and a steering device.

  A method using an end deflector is known as one of ball screw circulation methods. In this method, a circulation path is formed to circulate the ball in the nut. At both ends of the nut, an end deflector having a function of guiding the ball from the spiral groove of the nut and screw shaft to the circulation path or returning the ball from the circulation path to the spiral groove is attached (see, for example, Patent Document 1) ). The end deflector comprises a claw projecting into the helical groove of the screw shaft in order to scoop the ball into the end deflector.

JP 2012-154437 A

  In Patent Document 1, since the screw shaft is a movable body, a gap is provided between the claw portion and the spiral groove of the screw shaft so that the claw portion does not interfere with the screw shaft. That is, since a step is formed between the claw portion and the spiral groove of the screw shaft, it is known that a collision noise is easily generated when a ball coming through the spiral groove of the screw shaft hits this step. There's a problem.

  The present invention has been made to solve such problems, and a ball screw and a steering device capable of suppressing the collision noise between the end deflector and the ball when the ball enters the end deflector from the helical groove of the screw shaft. Intended to provide.

In order to solve the above problems, the present invention provides a nut, a screw shaft having a spiral groove formed on an outer peripheral surface, an end deflector attached to the nut, and a plurality of balls rolling along the spiral groove. The end deflector includes a pair of ball lifting portions provided across the width center of the spiral groove, and the pair of ball lifting portions has a width across the width center of the spiral groove. By supporting the ball at two places separated in a direction, the ball is lifted from the spiral groove, and the pair of ball lifting portions are located radially inward of the screw shaft than the center of the ball, the ball, when lifted from the spiral groove by contact of only two places of the pair of ball lifting part, be characterized by lifting the radially outward direction of the screw shaft .

  According to this ball screw, the impact when it abuts on the lifting portion is dispersed in two places. Therefore, even if a collision noise is generated when contacting the lifting portion, the collision noise is smaller than that when contacting the conventional claw portion. Since the lifting portion is located approximately 180 degrees opposite to the center of the ball, the bouncing behavior of the ball when contacting the lifting portion is also suppressed.

  If the pair of ball lifting portions are positioned radially outward of the groove ridge portion of the spiral groove of the screw shaft, the ball is lifted, and no contact with the screw shaft is considered, so The collision angle of the ball lifting portion can be set shallow and collision noise can be further suppressed.

  The pair of ball lifting portions are inclined so as to be displaced toward the width center of the spiral groove according to the radially inward direction of the screw shaft, and the distance between them is narrow according to the ball advancing direction If it comprises from a pair of inclined surface which becomes, a ball | bowl lifting part can be made into a simple structure, and a ball can be lifted smoothly.

  The end deflector is divided into a first member in which a semicircular passage having a cross-sectional semicircular shape continuous with the helical groove of the screw shaft is formed, and a second member having a semicircular passage having a circular cross-sectional shape continuous with the helical groove on the nut. When the first member is a first member, it extends along the ball advancing direction between the second member and the groove ridge of the screw shaft, and the width of the spiral groove across the width center of the spiral groove of the screw shaft. A pair of thin plate portions provided to be separated in a direction may be provided, and the inclined surfaces may be formed on the side surfaces of the thin plate portions facing each other.

  Further, according to the present invention, there is provided a steering apparatus including the ball screw, a motor for rotating the nut, and a steered shaft which moves integrally with the screw shaft and steers steered wheels. .

According to this steering device, it is possible to suppress the collision noise between the end deflector and the ball when the ball enters the end deflector from the spiral groove of the screw shaft.
The present invention also includes a nut, a screw shaft having a helical groove formed on the outer peripheral surface, an end deflector attached to the nut, and a plurality of balls rolling along the spiral groove of the screw shaft. The end deflector is a ball screw, and a pair of notches formed so as to smoothly guide the ball from the end of the helical groove of the nut, and a pair of sandwiching the width center of the helical groove of the screw shaft A ball lifting portion is provided, and the pair of ball lifting portions are located radially outward of the groove crest portion of the spiral groove of the screw shaft, and provided between the notch and the spiral groove of the screw shaft. , the pair of ball lifting portion, said supporting the ball at two positions spaced apart in the width direction across the width center of the spiral groove, the ball, when lifted from the helical groove, the pair Ball lifter By contact with only two places in, characterized in that lifting the radially outward direction of the screw shaft.

  According to the present invention, it is possible to suppress the collision noise between the end deflector and the ball when the ball enters the end deflector from the spiral groove of the screw shaft.

It is a schematic block diagram which shows an example of a steering device. It is sectional drawing which shows the helical groove of a nut, and the helical groove of a screw shaft. It is an external view of a ball screw concerning the present invention, and shows the state where an end deflector was attached to a nut (screw axis is not shown). It is an external view of a ball screw concerning the present invention, and shows a state before assembling an end deflector to a nut (screw axis is not shown). (A) is a perspective view of the state where the first member and the second member are assembled, (b) is a perspective view of the state before the first member and the second member are assembled, (c) is the first member and the second It is a top view of the state which attached two members. It is plane explanatory drawing of the nut and end deflector which were seen from the axial direction of the screw axis. FIG. 5 is a cross-sectional view of a screw groove and an end deflector of a screw shaft. (A), (b) and (c) are operation sectional views showing how the ball is lifted by the ball lifting portion. It is explanatory drawing which planarly expanded the helical groove of the screw shaft, seeing from radial outside.

  The ball screw 1 of the present invention is used, for example, in a rack assist type power steering apparatus 50 as shown in FIG. An example power steering apparatus 50 includes a steering wheel 51 operated by a driver, a steering shaft 52 integrally connected to the steering wheel 51, and an upper connecting shaft connected to the steering shaft 52 via a universal joint 53. 54, a lower connecting shaft 56 connected to the upper connecting shaft 54 via a universal joint 55, a lower connecting shaft 56 and a torsion bar 57 connected to each other, and a pinion shaft 58 having a pinion formed at the lower portion, and a pinion And rack shafts 59 to which left and right front wheels 61 are connected via tie rods 60 at both ends. The rack shaft 59 acts as a turning shaft for turning the wheels.

  A screw shaft 62 is mounted integrally with the rack shaft 59 between the rack shaft 59 and one tie rod 60, and the ball screw 1 is mounted on the screw shaft 62. A driven pulley 63 is axially attached to the outer periphery of the nut 21 of the ball screw 1, and a transmission belt 66 is engaged between the driven pulley 65 and the driven pulley 63 axially attached to the output shaft of the assist motor 64. It has been turned.

  In the power steering device 50 having the above configuration, the torque applied to the steering wheel 51 is detected by a torque sensor (not shown), and the motor 64 is drive-controlled by a control device (not shown) according to the detected torque. Thus, the torque generated by the motor 64 is controlled by the driver applied to the steering wheel 51 on the rack shaft 59 via the belt transmission mechanism including the drive pulley 65, the transmission belt 66, and the driven pulley 63 and the ball screw 1. It is transmitted as an aid to the force.

  The steering apparatus according to the present invention may be a so-called steer-by-wire type steering apparatus in which a reaction force actuator for giving the driver a sense of operation at the time of steering wheel operation and a steering actuator having a motor for driving the steering shaft are electrically connected. Ball screw 1 can be used.

Hereinafter, the ball screw 1 will be described in detail.
In FIG. 3 and FIG. 4, the ball screw 1 rolls along the screw groove 62 (FIG. 1) in which the nut 21 and the nut 21 are inserted and the spiral groove 36 is formed on the outer peripheral surface. A plurality of balls 41 (FIG. 2) and an end deflector 2 attached to a nut 21 are provided. In the following description, the advancing direction of the ball 41 refers to the direction in which the ball 41 enters the end deflector 2 from the spiral grooves 22 and 36 (FIG. 2).

"Nut 21"
The nut 21 is a cylindrical member, and as shown in FIG. 2, includes a spiral groove 22 that accommodates the ball 41 with the spiral groove 36 of the screw shaft 62. The cross-sectional shape of the spiral grooves 22 and 36 has, for example, a gothic arc shape having groove bottoms 34 and 37 respectively at pointed ends. The groove crest 35 of the spiral groove 22 and the groove crest 38 of the spiral groove 36 are separated by a distance s.

  Returning to FIG. 4, around the end of the nut 21, an annular inner end surface 23 formed around the edge of the opening through which the screw shaft 62 is inserted, and the outer edge of the inner end surface 23 The step wall surface 24 is formed in a step-like shape by the step wall surface 24 formed toward the end and the annular outer end surface 25 formed from the outer end of the step wall surface 24 radially outward of the axis O. A groove 26 for locking the snap ring 42 is formed in the step wall 24 all around. The outside in the direction of the axis O means a direction away from the central portion of the nut 21 in the direction of the axis O along the direction of the axis O, and the inside in the direction of the axis O means a direction approaching the center of the nut 21 in the axis O direction.

  The housing portion 27 for housing the end deflector 2 is formed by cutting out a part of each of the outer end surface 25 and the inner end surface 23 inward in the axial O direction at the end of the nut 21. The housing portion 27 extends from the inner peripheral surface of the nut 21 toward the outer peripheral surface, and is opposed to the first side wall surface 28 and the second side wall surface 29 facing each other, and an outer peripheral surface edge of the nut 21 at the first side wall surface 28 Of the first side wall surface 28, the second side wall surface 29, and the bottom wall surface 30 in the direction of the respective axes O in the direction of the bottom wall 30 formed across the outer peripheral surface of the second side wall 29 It is defined by the abutment surface 31 formed over the part.

  The first side wall surface 28, the second side wall surface 29, and the bottom wall surface 30 are formed along the axis O direction, and the abutting surface 31 is formed along a plane orthogonal to the axis O direction. Although the first side wall surface 28 and the second side wall surface 29 face each other, they do not have to be parallel to each other. The second side wall surface 29 is formed to be smoothly connected to the end 22 a of the spiral groove 22. The opening 33 of the circulation passage 32 faces the abutment surface 31. The circulation passage 32 is formed in the nut 21 along the direction of the axis O, and a similar opening 33 is formed at the opposite end of the nut 21.

"End deflector 2"
The end deflector 2 has a function to rectify the spiral movement of the ball 41 (FIG. 2) in the spiral grooves 22 and 36 and the axial O direction movement in the circulation path 32, that is, the spiral grooves 22 and 36 and the circulation path 32. A member having a function of changing the direction of the ball 41 between the two.

  As described mainly with reference to FIGS. 4 and 5, the end deflector 2 is formed with a passage 18 through which the ball 41 passes. In the present embodiment, mainly from the point of formability of the passage 18, the end deflector 2 is a first member in which a semicircular passage (referred to as a first half passage 11) having a cross section connected to the spiral groove 36 of the screw shaft 62 is formed. 3 and a second member 4 in which a semicircular passage (referred to as a second half passage 17) having a cross section continuous with the spiral groove 22 of the nut 21 is formed. The material of the end deflector 2 is not particularly limited, and may be a metal material, a synthetic resin material, or the like. When the end deflector 2 is made of, for example, a zinc material, a part can be formed by die casting.

  The first member 3 has a first side surface 6 formed so as to conform to the first side wall surface 28 as an outer surface substantially along the axis O direction, an outer side surface 13A formed so as to conform to the bottom wall surface 30, and a screw shaft 62 And a dividing surface 8 which is a surface that is in contact with the second member 4. The end surface of the first member 3 on the inner side in the direction of the axis O is formed as a contact surface 9 that abuts on the contact surface 31, and the end surface of the first member 3 on the outer side in the direction of the axis O is an end surface 10 to be pressed by the snap ring 42. It is formed. In the dividing surface 8, a first half passage 11 is formed which constitutes a half of the passage 18 of the ball 41. On a part of the inner surface 7, there is formed a claw portion 5 which bulges inward in the radial direction of the axis O and is positioned in the spiral groove 36 of the screw shaft 62. The claw portion 5 has a substantially semicircular shape having a size that does not interfere with the spiral groove 36.

  The second member 4 has a second side surface 12 formed following the second side wall surface 29 as an outer surface substantially along the axis O direction, an outer side surface 13B formed following the bottom wall surface 30, and a first member 3 and a dividing surface 14 which is a surface to be faced. The end surface of the second member 4 on the inner side in the direction of the axis O is formed as a contact surface 15 that abuts on the contact surface 31, and the end surface of the second member 4 on the outer side in the direction of the axis O is an end surface 16 to be pressed by the snap ring 42. It is formed. The divided surface 14 is formed with a second half passage 17 which constitutes one half of the passage 18 of the ball 41. A notch 40 is formed at the tip of the second half passage 17 so as to smoothly guide the ball 41 from the end 22 a of the spiral groove 22.

  An engaging projection 19 is formed on the divided surface 14 of the second member 4, and an engaging recess 20 is formed on the divided surface 8 of the first member 3. In the first member 3 and the second member 4, for example, when the engagement projection 19 engages with the engagement recess 20, for example, the divided surfaces 8 and 14 face each other, and both are integrated to form the end deflector 2. Configure The end faces 10 and 16 are connected in a flush manner, and the contact surfaces 9 and 15 are also connected in a flush manner. Then, by combining the first half passage 11 and the second half passage 17 inside the end deflector 2, a first passage 18A communicating with the spiral grooves 22 and 36, and the first passage 18A smoothly and substantially A passage 18 is formed, which includes a second passage 18B which is turned 90 degrees and formed along the axis O direction and is in communication with the opening 33 of the circulation passage 32. In addition, the structure which unifies the 1st member 3 and the 2nd member 4 is not specifically limited by the engagement method of the engagement protrusion part 19 and the engagement recessed part 20. FIG. Moreover, the structure which integrates the 1st member 3 and the 2nd member 4 may not be.

In the above configuration, when the ball 41 enters the end deflector 2 as shown in FIG.
(1) sandwiching state by the spiral groove 36 and the spiral groove 22;
(2) sandwiching state by the spiral groove 36 and the second half passage 17 of the second member 4;
(3) A clamping state of the first half passage 11 of the first member 3 and the second half passage 17 of the second member 4
Go through the order of
Regarding the transition from (1) to (2), the notch 40 (the second semi-passage 17 of the second member 4 does not form a gap or a step with respect to the end 22 a of the spiral groove 22 of the nut 21) By communicating smoothly as shown in FIG. 5), the ball 41 can be moved smoothly. However, for the transition from (2) to (3), since the screw shaft 62 is a movable body with respect to the end deflector 2, the first member 3 of the end deflector 2 and the spiral groove 36 of the screw shaft 62 There is no choice but to set a clearance t for contact avoidance. Therefore, as described above, the ball 41 easily collides with the claws 5 and the collision noise is easily generated due to the existence of the clearance t.

"Ball lifting part 71, 72"
To address this problem, the end deflector 2 of the present invention is provided with a pair of ball lifting portions 71, 72 (FIGS. 7 to 9) provided across the width center of the spiral groove 36 of the screw shaft 62. The pair of ball lifting portions 71, 72 lifts the ball 41 from the spiral groove 36 by supporting the balls 41 at two places separated in the width direction of the spiral groove 36 across the width center of the spiral groove 36.

  In the present embodiment, the ball lifting portions 71 and 72 are formed in the first member 3. In FIGS. 5 to 7, the first member 3 extends along the ball advancing direction between the second member 4 and the groove portion 38 of the screw shaft 62 and sandwiches the width center of the spiral groove 36 of the screw shaft 62. A pair of thin plate portions 73 and 74 are provided spaced apart in the width direction of the spiral groove 36. An inclined surface 75 is formed on the side surface of the thin plate portion 73 opposed to the thin plate portion 74, and an inclined surface 76 is formed on the side surface of the thin plate portion 74 opposed to the thin plate portion 73. The inclined surfaces 75, 76 are inclined so as to be displaced toward the width center of the spiral groove 36 according to the radially inward direction of the screw shaft 62, and from FIGS. 8 (a) to 8 (c) and FIG. As can be seen, the separation distance L between each other is made narrower as it goes in the ball advancing direction. The inclined surfaces 75, 76 constitute the ball lifting portions 71, 72. As understood from the above, the ball lifting portions 71 and 72 are positioned radially outward of the axis O with respect to the groove crest portion 38 of the spiral groove 36. The cross-sectional views of FIGS. 8A to 8C generally show cross sections A-A, B-B, and C-C in FIGS. 6 and 9, respectively. 8 (a) to 8 (c) and FIG. 9, in order to make it easy to understand how the separation distance L between the inclined surfaces 75 and 76 is displaced so as to be gradually narrowed, the inclined surfaces 75 and 76 should be stippled. It is illustrated.

  The inclined surfaces 75 and 76 may have a curved surface shape following the spherical surface of the ball 41, or may have a flat surface. As shown in FIG. 7, the distance w between the groove peak portion 38 of the screw shaft 62 and the thin plate portions 73 and 74 is set smaller than the distance u between the groove peak portion 38 of the screw shaft 62 and the ball center p. The radially inward edge of the inclined surfaces 75 and 76 is located radially inward of the ball center p. Therefore, when the ball 41 approaches the inclined surfaces 75, 76, the inclined surfaces 75, 76 contact the spherical surface below the center p of the ball 41 to lift the ball 41 from both sides, and the distance L in the traveling direction The ball 41 is gradually lifted up as

"Action"
When the ball 41 enters the end deflector 2 from the spiral grooves 22 and 36, as shown in FIGS. 8 (a) to 8 (c), the inclined surfaces 75 and 76 lift the ball 41 from both sides, and The ball 41 is gradually lifted as the separation distance L between the inclined surfaces 75 and 76 becomes narrower toward the end. Thereby, the ball 41 enters the passage 18 in the end deflector 2 without colliding with the tip of the claw 5.

  According to the present invention, when the pair of ball lifting portions 71 and 72 are provided, the impact when contacting the lifting portions 71 and 72 is dispersed in two places. Therefore, even if a collision noise occurs when contacting the lifting portions 71 and 72, the collision noise when contacting the conventional claws 5 is smaller. Since the lifting parts 71 and 72 are located approximately 180 degrees opposite to each other across the center p of the ball 41, the bouncing behavior of the ball 41 when it abuts on the lifting parts 71 and 72 is also suppressed.

  In addition, the ball lifting portions 71 and 72 of the present embodiment are located radially outward of the axis O relative to the groove crest portion 38 of the spiral groove 36. In the structure in which the ball 41 is covered by the conventional claws 5, the clearance t for avoiding contact must be set between the claws 5 and the spiral groove 36. Therefore, the collision angle with the ball 41 (traveling direction of the ball 41 And the angle of intersection with the tangential direction at the collision portion of the ball 41 becomes large, and the collision sound tends to be large. On the other hand, if the ball lifting portions 71 and 72 are positioned radially outward of the axis O with respect to the groove portion 38 of the spiral groove 36, the ball 41 is lifted and no contact with the screw shaft 62 is considered. Instead, the collision angles of the ball lifting portions 71 and 72 with respect to the ball 41 can be set extremely shallow. That is, it is possible to position around the tip of the ball lifting portions 71 and 72 substantially along the tangential direction of the spherical surface of the ball 41. Thereby, the generation of the collision sound can be almost eliminated.

  Further, the ball lifting portions 71 and 72 are inclined so as to be displaced toward the width center of the spiral groove 36 according to the radially inward direction of the screw shaft 62, and are separated from each other according to the ball advancing direction. If it comprises a pair of inclined surfaces 75 and 76 where L becomes narrow, the ball lifting parts 71 and 72 can be made into a simple structure, and the ball 41 can be lifted smoothly.

  Further, as in the present embodiment, when the first member 3 is provided with the pair of thin plate portions 73 and 74 and the inclined surfaces 75 and 76 are formed on the thin plate portions 73 and 74, the first member 3 and the second member are formed. The shape design of the end deflector 2 in the case of being divided into four parts becomes easy.

<Modification>
In the embodiment described above, the ball lifting portions 71 and 72 are formed on the first member 3 side, but may be formed on the second member 4 side. Further, the end deflector 2 may not be divided into the first member 3 and the second member 4 but may be integrally molded as a whole. Furthermore, as long as the balls 41 can be smoothly guided to the passage 18 in the end deflector 2 by the ball lifting portions 71 and 72, the claws 5 protruding into the spiral groove 36 may be eliminated.

1 Ball screw 2 End deflector 3 First member 4 Second member 21 Nut 22 Spiral groove (nut side)
36 Spiral groove (screw shaft side)
38 Grooves 41 Balls 71 and 72 Ball Lifts 73 and 74 Thin Plates 75 and 76 Inclined Surface

Claims (6)

A ball screw comprising: a nut; a screw shaft having a helical groove formed on an outer peripheral surface; an end deflector attached to the nut; and a plurality of balls rolling along the helical groove.
The end deflector comprises a pair of ball lifting portions provided across the width center of the spiral groove,
The pair of ball lifting portions lifts the ball from the spiral groove by supporting the ball at two places separated in the width direction across the width center of the spiral groove.
The pair of ball lifting portions are located radially inward of the center of the ball with respect to the center of the screw shaft, and when the balls are lifted from the spiral groove , two positions with the pair of ball lifting portions A ball screw characterized by being lifted in the radial outward direction of the screw shaft by only contact .   2. The ball screw according to claim 1, wherein the pair of ball lifting portions are positioned radially outward of a groove crest portion of the spiral groove of the screw shaft. The pair of ball lifters are:
Each of which is inclined so as to be displaced toward the width center of the spiral groove as the screw shaft is directed inward in the radial direction, and is formed of a pair of inclined surfaces in which the distance between them narrows as the ball travels; The ball screw according to claim 1 or 2, characterized in that: The end deflector is divided into a first member in which a semicircular passage in cross section continuous with the helical groove of the screw shaft is formed, and a second member in which a semicircular passage in cross section continuous with the helical groove of the nut is formed.
The first member extends along the ball advancing direction between the second member and the groove portion of the screw shaft, and is separated in the width direction of the spiral groove across the width center of the screw groove of the screw shaft. A pair of thin plate parts provided
The ball screw according to claim 3, wherein the inclined surfaces are formed on side surfaces of the thin plate portions facing each other. A ball screw according to any one of claims 1 to 4;
A motor for rotating the nut;
A steered shaft that moves integrally with the screw shaft and steers the steered wheels;
A steering apparatus comprising: A ball screw comprising: a nut; a screw shaft having a spiral groove formed on an outer peripheral surface; an end deflector attached to the nut; and a plurality of balls rolling along the spiral groove of the screw shaft.
The end deflector includes a notch formed so as to smoothly guide the ball from the end of the helical groove of the nut, and a pair of ball lifting portions provided across the width center of the helical groove of the screw shaft.
The pair of ball lifting portions are located radially outward of the groove crest portion of the spiral groove of the screw shaft, and provided between the notch and the spiral groove of the screw shaft.
The pair of ball lifting portions support the ball at two places separated in the width direction across the width center of the spiral groove, and when the ball is lifted from the spiral groove, the pair of balls A ball screw characterized in that the ball screw is lifted in the radial outward direction of the screw shaft by contact with only two places with a lifting portion .

Images